Abstract:

An optical compensation plate provided in a liquid crystal cell in which a
distance of a liquid crystal layer is held through a spacer, in which the
optical compensation plate is formed in such a way that a layer thickness
becomes thin toward a central portion from an end portion. As the spacer,
a spherical fine particle is employed. As a liquid crystal cell, a VA
mode liquid crystal cell is employed. Since the optical compensation
plate of the present invention has a thinner layer thickness in the
central portion in response to a decrease in a cell gap in the central
region of the liquid crystal cell, light leakage in the central region of
the liquid crystal layer can be prevented well.

Claims:

1. An optical compensation plate provided in a liquid crystal cell in
which a distance of a liquid crystal layer is held through a spacer,
wherein said optical compensation plate has a portion in which a layer
thickness becomes thin toward a central portion from an end portion.

2. The optical compensation plate according to claim 1, wherein said
optical compensation plate is formed into a rectangular shape and a layer
thickness becomes thin toward a central portion from both end portions in
a lateral direction.

3. The optical compensation plate according to claim 1, wherein the spacer
is composed of a fine particle which can move in the liquid crystal
layer.

4. The optical compensation plate according to claim 1, exhibiting a
relationship of nx>ny>nz,wherein nx, ny, and nz represent
refractive indexes in the direction of an X-axis, a Y-axis and a Z-axis,
respectively, and the X-axis is an axial direction in which the maximum
refractive index is shown in a plane, the Y-axis is an axial direction
perpendicular to the X-axis in the same plane, and the Z-axis represents
a thickness direction perpendicular to the X-axis and the Y-axis.

5. The optical compensation plate according to claim 1, wherein said
optical compensation plate is obtained by applying a long substrate film
successively with a birefringent material.

6. The optical compensation plate according to claim 5, wherein a width of
the long substrate film is 600 to 1500 mm, and said optical compensation
plate is obtained by applying the birefringent material, and then cutting
the long substrate film in a width direction.

7. The optical compensation plate according to claim 5, wherein the
birefringent material is a polymer solution including at least one
species of polymer selected from polyamide, polyimide, polyester,
polyetherketone, polyamide-imide and polyesterimide, and a solvent.

8. The optical compensation plate according to claim 5, wherein the
substrate film is a protective film of a polarizer.

9. A liquid crystal cell having the optical compensation plate according
to claim 1.

10. The liquid crystal cell according to claim 9, wherein said liquid
crystal cell is in a VA (vertical alignment) mode.

11. A liquid crystal display device having the liquid crystal cell
according to claim 9.

Description:

BACKGROUND OF THE INVENTION

[0001]1. Field of the Invention

[0002]The present invention relates to an optical compensation plate for a
liquid crystal cell in which a distance of a liquid crystal layer is held
through a spacer, a liquid crystal cell provided with the optical
compensation plate, and a liquid crystal display device.

[0003]2. Description of the Related Art

[0004]Hitherto, as a liquid crystal display device in a VA (vertical
alignment) mode, for example a transmissive liquid crystal display
device, a reflective liquid crystal display device, and a
semi-transmissive reflective liquid crystal display device have been
proposed in Japanese Unexamined Patent Publication Nos. 11-242226 and
2001-209065. As an application of the liquid crystal display device in
the VA mode, a liquid crystal television can be exemplified. Generally, a
liquid crystal cell of the liquid crystal display device is provided with
two liquid crystal cell substrates, spacers interposed between the two
substrates, and a liquid crystal material filled into a gap between the
two substrates. In the liquid crystal cell, a thickness (cell gap) of a
liquid crystal layer, in which the liquid crystal material is filled, is
kept constant through a spacer.

[0005]This liquid crystal layer, in which the liquid crystal material is
filled, itself has a birefringent property and a retardation. An optical
compensation plate capable of canceling (compensating) the retardation of
the liquid crystal layer is laminated on the liquid crystal cell for
improving a viewing angle characteristic resulting from this retardation.

[0006]As the optical compensation plate, for example, a biaxial optical
film having a relationship of nx>ny>nz is known. This optical
compensation plate is a film formed by, for example, applying a
non-liquid crystal material selected from polyamide, polyimide,
polyester, polyetherketone, polyamide-imide, polyesterimide and the like
onto a transparent film typified by triacetyl cellulose, as described for
example in Japanese Unexamined Patent Publication No. 2004-46065.

[0007]This optical compensation plate is formed so as to have a uniform
thickness, and laminated on and bonded to, for example, the backlight
side of the liquid crystal cell substrate.

[0008]However, even when the retardation of the liquid crystal layer is
compensated by laminating the above-mentioned optical compensation plate,
light leakage may occur in a central region of the liquid crystal cell.
If the light leakage occurs, there is a problem that in viewing a liquid
crystal display surface in a black-display state from an angle, the
black-display level is deteriorated. Particularly in a relatively large
liquid crystal cell, reduction in the black-display level in a central
region of the display surface is apt to occur.

SUMMARY OF THE INVENTION

[0009]It is an object of the present invention to provide an optical
compensation plate which can compensate well a liquid crystal cell,
particularly a large liquid crystal cell, to improve a viewing angle
characteristic, a liquid crystal cell, and a liquid crystal display
device.

[0010]The present inventors made earnest investigations concerning the
above-mentioned problem, and consequently found that the problem results
from partial change of the cell gap of the liquid crystal cell and
therefore an optical compensation plate having a uniform thickness cannot
compensate the whole area of the liquid crystal layer. These findings
have now led to completion of the present invention.

[0011]That is, in the liquid crystal cell used in a liquid crystal display
device, a cell gap is kept constant through a spacer as described above.
Spacers are almost evenly located at the time when a liquid crystal cell
is manufactured. However, if external bending stress is applied to the
liquid crystal cell after production, spacers positioned in a central
region of the liquid crystal cell move to the end side of the liquid
crystal cell, or spacers positioned in the central region are deformed by
compression or immersed in a color filter or the like. Consequently, the
cell gap in the central region of the liquid crystal cell becomes thin
(small). Particularly, changes in the cell gap in the central region are
remarkable with upsizing of the liquid crystal display device. Although
the cell gap in the central region of the liquid crystal cell thus
changes to be thin, conventionally, an optical compensation plate that
has the thickness with a high uniformity has been employed as the optical
compensation plate provided for the liquid crystal cell. Therefore, the
conventional optical compensation plate cannot adequately compensate the
liquid crystal cell in which the cell gap in the central region has
become thin, and this causes light leakage to occur.

[0012]The present invention has been made under the above-mentioned
findings, and provides an optical compensation plate provided in a liquid
crystal cell in which a distance of a liquid crystal layer is held
through a spacer, which has a portion in which a layer thickness becomes
thin toward a central portion from an end portion.

[0013]The above-mentioned optical compensation plate is attached to the
liquid crystal cell in which the distance of a liquid crystal layer is
held through a spacer before being used.

[0014]As described above, when external bending stress is applied to the
liquid crystal cell in which a cell gap is held through a spacer, the
cell gap becomes thin in a central region of the liquid crystal cell.
Consequently, an absolute value of retardation of a liquid crystal layer
is relatively small in the central region where the cell gap is thin. On
the other hand, since the optical compensation plate of the present
invention is formed in such a way that the layer thickness becomes thin
toward a central portion from an end portion, the absolute value of
retardation also becomes small in the central region of the optical
compensation plate.

[0015]Thus, by providing the liquid crystal cell with the optical
compensation plate having a central portion formed so as to be thinner in
response to a decrease in the retardation in the central region of the
liquid crystal cell, light exiting the central region of the liquid
crystal layer can be compensated well.

[0016]The optical compensation plate of the present invention can prevent
light leakage in the central region of the liquid crystal cell, and can
prevent light leakage well particularly in the central region of a liquid
crystal display device having a large screen to improve a viewing angle
characteristic.

[0017]In addition, a preferred aspect of the present invention provides
the optical compensation plate formed into a rectangular shape in which a
layer thickness becomes thin toward a central portion from both end
portions in a lateral direction.

[0018]Further, a preferred aspect of the present invention provides the
optical compensation plate in which the spacer is composed of a fine
particle which can move in the liquid crystal layer.

[0019]Further, a preferred aspect of the present invention provides the
optical compensation plate exhibiting a relationship of nx>ny>nz,
wherein nx, ny, and nz represent refractive indexes in the direction of
an X-axis, a Y-axis and a Z-axis, respectively, and the X-axis is an
axial direction in which the maximum refractive index is shown in a
plane, the Y-axis is an axial direction perpendicular to the X-axis in
the same plane, and the Z-axis represents a thickness direction
perpendicular to the X-axis and the Y-axis.

[0020]In addition, a preferred aspect of the present invention provides
the optical compensation plate obtained by coating a long substrate film
successively with a birefringent material.

[0021]Further, a preferred embodiment of the present invention provides
the optical compensation plate obtained by applying the birefringent
material, and then cutting the long substrate film in a width direction
in which a width is 600 to 1500 mm.

[0022]In addition, a preferred aspect of the present invention provides
the optical compensation plate in which the birefringent material is a
polymer solution including at least one species of polymer selected from
polyamide, polyimide, polyester, polyetherketone, polyamide-imide and
polyesterimide, and a solvent.

[0023]Further, a preferred aspect of the present invention provides the
optical compensation plate in which the substrate film is a protective
film of a polarizer.

[0025]Further, the present invention provides a liquid crystal display
device having the liquid crystal cell having the optical compensation
plate.

BRIEF DESCRIPTION OF THE DRAWINGS

[0026]FIG. 1A is a front view showing an embodiment of a liquid crystal
cell of the present invention, and FIG. 1B is a sectional view taken on
line A-A of FIG. 1A;

[0027]FIG. 2A is a front view showing an embodiment of an optical
compensation plate of the present invention, and FIG. 2B is a sectional
view taken on line B-B of FIG. 2A;

[0028]FIGS. 3A and 3B are sectional views showing another embodiment of
the liquid crystal cell of the present invention;

[0029]FIG. 4 is a side view, partially including a sectional view, showing
an embodiment of a die coater apparatus used for producing the optical
compensation plate;

[0030]FIG. 5 is a perspective view showing an embodiment of a slot die of
the die coater apparatus of FIG. 4;

[0031]FIG. 6 is an exploded perspective view of the slot die of FIG. 5;

[0032]FIGS. 7A and 7B are oblique front views of the slot die of FIG. 5,
FIG. 7A shows a state in which an actuator is not started, and FIG. 7B
shows a state in which the actuator is started;

[0033]FIG. 8 is a side view, partially including a sectional view, showing
a state of applying a material with the die coater apparatus of FIG. 4,
in which an alternate long and short dash line shows a central portion of
the die main body deformed by starting of the actuator;

[0034]FIG. 9 shows a variation example of the die coater apparatus, FIG.
9A is a perspective view thereof, and FIG. 9B is a front view thereof;
and

[0035]FIG. 10 is a partially simplified perspective view showing a cutting
direction of a long substrate film on which the optical compensation
plate is laminated.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0036]Hereinafter, embodiments of the present invention will be described.

[0037]As shown in FIG. 1A, a display surface of a liquid crystal cell 1 of
the present invention is shaped like a rectangle in front view, for
example. The liquid crystal cell 1 is formed in such a way that a
length-to-width ratio of the display surface is, for example, about 3:4
to 10:16 to adapt to a liquid crystal television. A size of the display
surface of the liquid crystal cell 1 is not particularly limited.
However, since the optical compensation plate of the present invention is
suitable for compensating a relatively large liquid crystal cell, the
display surface of the liquid crystal cell 1 is preferably about 600 mm
to 1500 mm wide.

[0038]This the liquid crystal cell 1 includes, for example as shown in
FIG. 1B, a pair of liquid crystal cell substrates 2, 2, spacers 3
interposed between the liquid crystal cell substrates 2, 2, a liquid
crystal material (not shown) filled in a liquid crystal layer 5 formed
between the pair of the liquid crystal cell substrates 2, 2, and an
electrode element (not shown) such as a TFT substrate for driving the
liquid crystal material provided on the inner surface side (liquid
crystal layer side) of one liquid crystal cell substrate 2. The display
surface of the liquid crystal cell 1 is shaped like a rectangle in which
a width is longer than a length. An optical compensation plate 7 is
provided on the outer surface side of the liquid crystal cell substrate 2
on the viewing side of this liquid crystal cell 1. In this optical
compensation plate 7, a central portion is formed so as to have a thinner
thickness. Polarizers 8 are provided on the outer surface of the optical
compensation plate 7 and on the outer surface of the other liquid crystal
cell substrate 2, respectively. On both sides of these polarizers 8,
protective films 9, 9 are provided. Accordingly, the polarizers 8 are
laminated on the outer surface of the optical compensation plate 7 and
the outer surface of the other liquid crystal cell substrate 2 across the
protective films 9.

[0039]The polarizer 8 and the protective film 9, 9 are formed in a uniform
layer thickness. However, in FIG. 1B, the polarizer 8 and the protective
film 9 provided on the viewing side are shown in a curve because the
polarizer 8 and the protective film 9 are laminated on the optical
compensation plate 7 in which the central portion is formed so as to have
a thinner thickness.

[0040]Further, the protective film 9 and the polarizer 8 are not
particularly limited, and as the protective film 9 and the polarizer 8,
publicly known substances can be used. Specific examples of the
protective film 9 include substances exemplified as a substrate film
described later. Specific examples of the polarizer 8 are also described
later. In addition, as the protective film 9, films subjected to, for
example, a hard coat treatment, an anti-reflection treatment, and
publicly known treatments aimed at preventing sticking, diffusing or
antiglare can also be used.

[0041]As the liquid crystal cell 1 of the present invention, a
constitution of a publicly known liquid crystal cell can be employed as
long as it is a liquid crystal cell in which a distance of the liquid
crystal layer 5 is held through the spacer 3. The liquid crystal cell of
the present invention may have other constituents (not shown) publicly
known such as a liquid crystal cell in which a color filter is provided
on the liquid crystal cell substrate 2 on the viewing side, and a liquid
crystal cell in which a rubbing alignment layer is provided on the liquid
crystal layer 5 in addition to the above-mentioned constitution.

[0042]The liquid crystal cell substrate 2 is not particularly limited as
long as it has high transparency. As the liquid crystal cell substrate 2,
transparent flexible materials, for example, transparent glass plates
such as soda-lime glass, low alkali borosilicate glass, alkali-free
aluminoborosilicate glass and the like; and optical resin plates such as
polycarbonate, polymethyl methacrylate, polyethylene terephthalate, epoxy
resin and the like can be used.

[0043]The spacer 3 is provided to hold a cell gap of the liquid crystal
layer 5. As the spacers 3, a spacer (also referred to as a bead spacer)
formed by dispersing a fine particle in the liquid crystal layer 5, and a
spacer (also referred to as a post spacer) formed by locating pillar
bodies in the liquid crystal layer 5 are known. In the present invention,
both spacers can be used. The former spacer 3 including a fine particle
is not fixed to the liquid crystal cell substrate 2 and is a
non-stationary spacer which can move in the liquid crystal layer 5.
Therefore, in the liquid crystal cell 1 having the spacer 3, the cell gap
in the central region tends to become thin by the application of bending
stress. Accordingly, it is particularly effective to apply the optical
compensation plate 7 of the present invention to the liquid crystal cell
1 employing the non-stationary spacer 3.

[0044]A material of the above-mentioned fine particle is not particularly
limited, and a plastic particle, a silica particle and the like can be
employed. A shape of the fine particle is also not particularly limited,
and those having a publicly known shape such as a spherical, a
cylindrical, a rectangular solid, a cubic, or a semi-spherical can be
used. However, when a spherical fine particle or a cylindrical fine
particle, as shown in the figures, is used as the spacer 3, the fine
particle especially tends to move in the liquid crystal layer 5.
Accordingly, it is particularly effective to apply the optical
compensation plate 7 of the present invention to the liquid crystal cell
1 employing a spherical fine particle or a cylindrical fine particle as
the spacer 3. A diameter of the fine particle is appropriately set in
accordance with the thickness of the liquid crystal layer 5, and
generally, a diameter of about 3 to 15 μm is employed. In addition,
number of fine particles to be dispersed per unit area is not
particularly limited. However, since too many fine particles cause a
problem of disturbing the alignment of a liquid crystal material,
generally, the number of fine particles to be dispersed is preferably
about 100 to 300 pcs. per 1 square millimeters.

[0045]As the spacer (post spacer) formed by locating a pillar body in the
liquid crystal layer, for example, a spacer, one end face of which is
fixed to the one liquid crystal cell substrate, can be exemplified. This
spacer can be formed, for example, by a method in which a photosensitive
resin material is applied and a pillar body is formed on a black matrix
of a color filter by a photolithography process.

[0046]A publicly known liquid crystal material is filled in the liquid
crystal layer in which non-stationary spacers are provided. The liquid
crystal material is not particularly limited, but it is preferred from
the viewpoint of high contrast to use a liquid crystal material in a VA
(vertical alignment) mode in which the liquid crystal material is aligned
almost perpendicularly to the liquid crystal cell substrate during a
no-voltage time. A liquid crystal cell in which such liquid crystal
material is filled is generally referred to as a VA mode liquid crystal.

[0047]Next, the optical compensation plate 7 of the present invention will
be described.

[0048]The optical compensation plate 7 is mainly used for canceling the
retardation of a liquid crystal layer and composed of a birefringence
layer exhibiting a prescribed retardation.

[0049]As shown in FIG. 2B, the optical compensation plate 7 has a portion
in which a layer thickness becomes thin toward a central portion from an
end portion. The optical compensation plate 7 includes at least a
compensation plate formed so as to have a thinner central portion than a
peripheral portion or a thinner central portion than both end portions in
a lateral direction.

[0050]In the example shown in FIG. 2A, the optical compensation plate 7 is
shaped like a rectangle of nearly identical shape and size with a display
surface of the liquid crystal cell 1 in front view. The optical
compensation plate 7 is formed so as to have a thickness distribution
which becomes thin toward a central portion from both end portions in a
lateral direction. Accordingly, as shown in the figure, one surface of
the optical compensation plate 7 is formed in the form of a side of a
cylinder (at least one edge in a thickness direction is arc-shaped).

[0051]The optical compensation plate 7 may be constructed from a
birefringence layer of one layer or a laminated body formed by laying two
or more birefringence layers one on top of another. In addition, the
optical compensation plate 7 may be provided between the protective film
9 and the polarizer 8.

[0052]The optical compensation plate 7 is provided on the viewing side of
the liquid crystal cell 1, as shown in FIG. 1B, but arrangement of the
optical compensation plate 7 is not limited to this. For example, as
shown in FIG. 3A, the optical compensation plate 7 may be provided on the
side (backlight side) opposite to the viewing side of the liquid crystal
cell 1. Further, as shown in FIG. 3B, the optical compensation plate 7
may be provided on both sides of the liquid crystal cell 1.

[0053]A thickness of the optical compensation plate 7 is appropriately set
in consideration of materials composing the optical compensation plate 7
and the retardation of the liquid crystal layer 5. The thickness at an
end of the optical compensation plate 7 is preferably set at 1 to 40
μm, more preferably set at 2 to 30 μm, and furthermore preferably
set at 2 to 15 μm from the viewpoint of realizing a low-profile liquid
crystal display device.

[0054]Further, the thickness at a central portion of the optical
compensation plate 7 is not particularly limited. The reason for this is
that the thickness at a central portion is to be appropriately set in
response to the extent to which the cell gap in the central region of the
liquid crystal layer 5 becomes thin due to the movement of the spacer 3.
However, it is unlikely that the cell gap in the central region of the
liquid crystal layer 5 changes extremely thin compared with the cell gap
in the end portion of the liquid crystal layer 5. Therefore, it is
preferred that the thickness in the central portion of the optical
compensation plate 7 is generally set so as to be 0.6 times to 0.95 times
larger than the thickness at an end portion, more preferably 0.7 times to
0.9 times, and furthermore preferably 0.75 times to 0.9 times.

[0055]In the above-mentioned liquid crystal cell 1, a cell gap is held
through the spacer 3. However, since bending stress is applied to the
liquid crystal cell 1 after production and thereby the spacers 3 in the
central region of the liquid crystal cell 1 move or are deformed by
compression, the cell gap in the central region of the liquid crystal
cell 1 becomes thin. Particularly, in a liquid crystal cell 1 having a
relatively large rectangular display surface of about 600 mm to 1500 mm
wide, the cell gap in the central region in a lateral direction tends to
become thin compared with those in both end portions in a lateral
direction.

[0056]When the cell gap thus changes, an absolute value of retardation of
the liquid crystal layer 5 becomes large at the end side and becomes
small in the central region. Therefore, a retardation distribution
becomes nonuniform in the respective region of one liquid crystal layer.

[0057]In the present invention, the optical compensation plate 7 provided
in such liquid crystal cell 1 is formed in such a way that the layer
thickness becomes thin toward a central portion from an end portion.
Therefore, the absolute value of retardation of the optical compensation
plate 7 becomes small toward the central portion.

[0058]Accordingly, even when the absolute value of retardation
(particularly retardation in a thickness direction) in the central region
of the liquid crystal cell 1 becomes small due to changes in the cell
gaps, it is possible to compensate the central region of the liquid
crystal cell 1 well to prevent light leakage by providing an optical
compensation plate 7 having a central portion formed thinner.

[0059]Incidentally, the cell gap on the end side of the liquid crystal
cell 1 does not substantially change, the end side of the liquid crystal
cell 1 can also be compensated well by the above-mentioned optical
compensation plate 7.

[0060]Thus, the optical compensation plate 7 of the present invention has
a thinner central portion formed in response to a decrease in the
retardation in the central region of the liquid crystal cell 1, it can
compensate the whole area of the liquid crystal layer 5 well. The liquid
crystal cell 1 and the liquid crystal display device, provided with the
optical compensation plate 7, are superior in a viewing angle
characteristic.

[0061]In addition, the optical compensation plate 7 is formed in such a
way that the layer thickness becomes thin gradually toward a central
portion from an end portion. Therefore, there is no possibility that
streaked patterns appear on a display surface in displaying images on a
liquid crystal display device.

[0062]As the above-mentioned optical compensation plate 7, one exhibiting
an optical property of nx>ny>nz or nx≈ny>nz is
preferred. Herein, nx, ny, and nz represent refractive indexes of an
X-axis, a Y-axis and a Z-axis, respectively, in the optical compensation
plate, and the X-axis is an axial direction in which the maximum
refractive index is shown in a plane of the compensation plate, the
Y-axis is an axial direction perpendicular to the X-axis in the same
plane, and the Z-axis represents a thickness direction perpendicular to
the X-axis and the Y-axis.

[0063]By locating the optical compensation plate exhibiting the
above-mentioned optically biaxial property of nx>ny>nz between the
liquid crystal cell of the liquid crystal display device and the
polarizer, the viewing angle of the liquid crystal display device can be
widened.

[0065]A material for forming the optical compensation plate is not
particularly limited and conventionally known materials can be employed.
In addition, as criteria by which the material for forming the optical
compensation plate is selected, it is preferred to select, for example, a
material, in which the birefringence in forming the optical compensation
plate becomes relatively high.

[0066]The material for forming the optical compensation plate is
preferably, for example, a non-liquid crystal material, particularly a
non-liquid crystal polymer. Such non-liquid crystal material forms, for
example, a film exhibiting an optically uniaxial property of nx>nz or
ny>nz by nature of the non-liquid crystal polymer itself as distinct
from the liquid crystal material. Therefore, for example, a substrate to
be used in preparing the optical compensation plate is not limited to an
aligned substrate to be used in the case of the liquid crystal material.
That is, as a substrate in preparing the optical compensation plate using
the non-liquid crystal polymer, for example, a not-yet-aligned substrate
can be employed, and even when the not-yet-aligned substrate is used, the
step of applying or laminating an alignment layer onto the surface of the
substrate can be omitted.

[0067]As the above-mentioned non-liquid crystal polymer, for example,
polymers such as polyamide, polyimide, polyester, polyetherketone,
polyamide-imide and polyesterimide are preferred since these polymers are
superior in heat resistance, chemical resistance, and transparency and
rich in rigidity. Any one species of these polymers may be used alone.
These polymers may be used as a mixture of two or more species having
different functional groups, such as a mixture of polyaryletherketone and
polyamide. Among such polymers, polyimide is particularly preferred since
it has high transparency, a high aligning property, and a high stretching
property.

[0068]A molecular weight of the above-mentioned polymer is not
particularly limited, but for example, a weight average molecular weight
(Mw) is preferably in a range of 1000 to 1000000, and more preferably in
a range of 2000 to 500000.

[0069]As the polyimide, for example, polyimide which has a high in-plane
aligning property and is soluble in an organic solvent is preferred.
Specifically, for example, a polymer disclosed in Japanese Unexamined
Patent Publication No. 2000-511296, which includes a polycondensation
product of 9,9-bis(aminoaryl)fluorene and aromatic tetracarboxylic
dianhydride and includes one or more repeat units expressed by the
following formula (1):

##STR00001##

can be used.

[0070]In the formula (1), each of groups of R3 to R6 is at least
one species of a substituent selected independently from the group
consisting of hydrogen, halogen, a phenyl group, a phenyl group
substituted by 1 to 4 halogen atoms or a C1 to C10 alkyl group,
and a C1 to C10 alkyl group. Each of groups of R3 to
R6 is preferably at least one species of a substituent selected
independently from the group consisting of halogen, a phenyl group, a
phenyl group substituted by 1 to 4 halogen atoms or a C1 to C10
alkyl group, and a C1 to C10 alkyl group.

[0071]In the formula (1), Z is, for example, a tetravalent C6 to
C20 aromatic group, and preferably a pyromellitic group, a
polycyclic aromatic group, a derivative of a polycyclic aromatic group,
or a group expressed by the following formula (2):

##STR00002##

[0072]In the formula (2), Z' is, for example, a covalent bond, a
C(R7)2 group, a CO group, an oxygen (O) atom, a sulfur (S)
atom, an SO2 group, an Si(C2H5)2 group, or an
NR8 group, and when number of Z's is two or more, these Z's are the
same or different. In addition, w represents an integer of 1 to 10.
R7 is independently hydrogen or a C(R9)3. R8 is
hydrogen, an alkyl group having 1 to about 20 carbon atoms, or a C6
to C20 aryl group, and when number of R8s is two or more, these
R8s are the same or different. R9s are independently hydrogen,
fluorine, or chlorine.

[0073]Examples of the polycyclic aromatic group include, for example, a
tetravalent group derived from naphthalene, fluorene, benzofluorene, or
anthracene. In addition, examples of a substituted derivative of the
foregoing polycyclic aromatic group include a polycyclic aromatic group
substituted by at least a group selected from the group consisting of a
C1 to C10 alkyl group, a fluorinated derivative thereof and
halogen (fluorine, chlorine, or the like).

[0074]In addition to these, examples of the polycyclic aromatic group
include a homopolymer having a repeat unit expressed by the following
general formula (3) or (4), and polyimide having a repeat unit expressed
by the following general formula (5), which are described in Japanese
Unexamined Patent Publication No. 8-511812. In addition, the polyimide of
the following formula (5) is a preferred form of the homopolymer of the
following formula (3).

##STR00003##

[0075]In the general formulas (3) to (5), G and G' represent, for example,
a group, respectively, selected independently from the group consisting
of a covalent bond, a CH2 group, a C(CH3)2 group, a
C(CF3)2 group, a C(CX3)2 group (X is halogen), a CO
group, an oxygen (O) atom, a sulfur (S) atom, an SO2 group, an
Si(CH2CH3)2 group and an N(CH3) group, and these G
and G' may be the same or different.

[0076]In the formulas (3) and (5), L is a substituent and its subscripts d
and e represent the number of the substituents. The substituent L is, for
example, halogen, a C1 to C3 alkyl group, a C1 to C3
halogenated alkyl group, a phenyl group, or a substituted phenyl group,
and when number of the substituent Ls is two or more, these Ls are the
same or different. Example of the foregoing substituted phenyl group
include a substituted phenyl group having at least one species of a
substituent selected from the group consisting of halogen, a C1 to
C3 alkyl group, and a C1 to C3 halogenated alkyl group. In
addition, examples of the foregoing halogen include fluorine, chlorine,
bromine, and iodine. The subscript d is an integer of 0 to 2, and the
subscript e is an integer of 0 to 3.

[0077]In the formulas (3) to (5), Q is a substituent and its subscript f
represents the number of the substituent. The substituent Q is, for
example, an atom or a group selected from the group consisting of
hydrogen, halogen, an alkyl group, a substituted alkyl group, a nitro
group, a cyano group, a thioalkyl group, an alkoxy group, an aryl group,
a substituted aryl group, an alkylester group and a substituted
alkylester group, and when number of the substituent Qs is two or more,
these Qs are the same or different. Examples of the foregoing halogen
include fluorine, chlorine, bromine, and iodine. Examples of the
foregoing substituted alkyl group include a halogenated alkyl group. In
addition, examples of the foregoing substituted aryl group include a
halogenated aryl group. The subscript f is an integer of 0 to 4, the
subscript g is an integer of 0 to 3, and the subscript h is an integer of
1 to 3. In addition, the subscript g and h are preferably larger than 1.

[0078]In the formula (4), each of groups of R10 and R11 is a
substituent selected independently from the group consisting of hydrogen,
halogen, a phenyl group, a substituted phenyl group, an alkyl group, and
a substituted alkyl group. Among these groups, preferably, each of groups
of R10 and R11 is independently a halogenated alkyl group.

[0079]In the formula (5), M1 and M2 are the same or different,
and they are, for example, halogen, a C1 to C3 alkyl group, a
C1 to C3 halogenated alkyl group, a phenyl group, or a
substituted phenyl group. Examples of the foregoing halogen include
fluorine, chlorine, bromine, and iodine. In addition, examples of the
foregoing substituted phenyl group include a substituted phenyl group
having at least one species of a substituent selected from the group
consisting of halogen, a C1 to C3 alkyl group, and a C1 to
C3 halogenated alkyl group.

[0080]Specific examples of polyimide expressed by the formula (3) include
compounds having a repeat unit expressed by the following formula (6):

##STR00004##

[0081]Furthermore, examples of the foregoing polyimide include copolymers
formed by appropriately copolymerizing acid dianhydride or diamine other
than the skeleton (repeat unit) described above.

[0086]Examples of the diamine include aromatic diamine. Specific examples
of the aromatic diamine include benzene diamine, diaminobenzophenone,
naphthalenediamine, and heterocyclic aromatic diamine.

[0087]Examples of the benzene diamine include diamines selected from the
group consisting of benzene diamines such as o-, m- or
p-phenylenediamine, 2,4-diaminotoluene, 1,4-diamino-2-methoxybenzene,
1,4-diamino-2-phenylbenzene and 1,3-diamino-4-chlorobenzene. Examples of
the diaminobenzophenone include 2,2'-diaminobenzophenone and
3,3'-diaminobenzophenone. Examples of the naphthalenediamine include
1,8-diaminonaphthalene and 1,5-diaminonaphthalene. Examples of the
heterocyclic aromatic diamine include 2,6-diaminopyridine,
2,4-diaminopyridine, and 2,4-diamino-S-triazine.

[0089]Examples of the foregoing polyetherketone, a material for forming an
optical compensation plate, include polyaryletherketone described in
Japanese Unexamined Patent Publication No. 2001-49110, which is expressed
by the following general formula (7):

##STR00005##

[0090]In the formula (7), X represents a substituent and its subscript q
represents the number of the substituents. The substituent X is, for
example, a halogen atom, a lower alkyl group, a halogenated alkyl group,
a lower alkoxy group, or a halogenated alkoxy group, and when number of
the substituent Xs is two or more, these Xs are the same or different.

[0091]Examples of the foregoing halogen atom include a fluorine atom, a
bromine atom, a chlorine atom and an iodine atom, and among these halogen
atoms, the fluorine atom is preferred. As the foregoing lower alkyl
group, for example, C1 to C6 lower alkyl groups having a
straight chain or branched chain are preferred, and C1 to C4
lower alkyl groups having a straight chain or branched chain are more
preferred. As the lower alkyl group, specifically, a methyl group, an
ethyl group, a propyl group, an isopropyl group, a butyl group, an
isobutyl group, a sec-butyl group, and a tert-butyl group are preferred,
and a methyl group and an ethyl group are particularly preferred.
Examples of the foregoing halogenated alkyl group include halides of the
foregoing lower alkyl group, such as a trifluoromethyl group. As the
foregoing lower alkoxy group, for example, C1 to C6 alkoxy
groups of a straight chain or branched chain are preferred, and C1
to C4 alkoxy groups of a straight chain or branched chain are more
preferred. As the lower alkoxy group, specifically, a methoxy group, an
ethoxy group, a propoxy group, an isopropoxy group, a butoxy group, an
isobutoxy group, a sec-butoxy group, and a tert-butoxy group are
preferred, and a methoxy group and an ethoxy group are particularly
preferred. Examples of the foregoing halogenated alkoxy group include
halides of the foregoing lower alkoxy group, such as a trifluoromethoxy
group.

[0092]In the formula (7), the subscript q is an integer of 0 to 4. In the
formula (7), polyaryletherketone, in which the subscript q is 0 and a
carbonyl group and an oxygen atom of ether, bonded to both ends of a
benzene ring, exist at a para position, respectively, is preferred.

[0093]In addition, in the formula (7), R1 is a group expressed by the
following formula (8), and the subscript m in the formula (7) is an
integer of 0 or 1.

##STR00006##

[0094]In the formula (8), X' represents a substituent and is similar to,
for example, the X in the formula (7). In the formula (8), when number of
the substituent X's is two or more, these X's are the same or different.
The subscript q' represents the number of the foregoing substituents X',
and is an integer of 0 to 4 and preferably 0. In addition, the subscript
p is an integer of 0 or 1.

[0095]In the formula (8), R2 represents a bivalent aromatic group.
Examples of the bivalent aromatic group include an o- or m- or
p-phenylene group; bivalent groups derived from naphthalene, biphenyl,
anthracene, o- or m- or p-terphenyl, phenanthrene, dibenzofuran,
biphenylether and biphenylsulfone; and the like. In these bivalent
aromatic groups, hydrogen directly bonded to the aromatic may be replaced
with a halogen atom, a lower alkyl group or a lower alkoxy group. Among
these, an aromatic group selected from the group consisting of the
following formulas (9) to (15):

##STR00007##

is preferred as an R2 group.

[0096]In addition, in the above formula (7), as the group R1, a group
expressed by the following formula (16) is preferred, and in the
following formula (16), R2 and p are identical to those of the
foregoing formula (8).

##STR00008##

[0097]Furthermore, in the above formula (7), n represents a polymerization
degree, and this polymerization degree ranges from 2 to 5000, preferably
from 5 to 500. In addition, the polymerization may consist of repeat
units having the same structure, or may consist of repeat units having
different structures. In the latter case, the form of the polymerization
of the repeat units may be block polymerization or may be random
polymerization.

[0098]Further, it is preferred that an end of polyaryletherketone
expressed by the above formula (7) is fluorine on the side of a
p-tetrafluorobenzoylene group and a hydrogen atom on the side of an
oxyalkylene group. Such polyaryletherketone can be expressed by, for
example, the following general formula (17). Further, in the following
formula (17), n represents the same polymerization degree as in the
formula (7).

##STR00009##

[0099]Specific examples of polyaryletherketone expressed by the above
formula (7) include compounds having a repeat unit expressed by the
following formulas (18) to (21), wherein n represents the same
polymerization degree as in the above formula (7).

##STR00010##

[0100]In addition to these compounds, examples of the foregoing polyamide
or polyester, which is a material for forming an optical compensation
plate, include polyamide and polyester described in Japanese Unexamined
Patent Publication No. 10-508048. A repeat unit of the polyamide and
polyester can be expressed, for example, by the following general formula
(22):

##STR00011##

[0101]In the formula (22), each of Ys is O or NH. In addition, each of Es
is, for example, at least a group selected from the group consisting of a
covalent bond, a C2 alkylene group, a halogenated C2 alkylene
group, a CH2 group, a C(CX3)2 group (X is halogen or
hydrogen), a CO group, an oxygen (O) atom, a sulfur (S) atom, an SO2
group, an Si(R)2 group and an N(R) group, and these groups E may be
the same or different. In the foregoing groups E, R is at least one
species of a C1 to C3 alkyl group and a C1 to C3
halogenated alkyl group and is positioned at a meta position or a para
position with respect to a carbonyl functional group or a group Y.

[0102]In addition, in the formula (22), each of A and A: is a substituent
and their subscripts t and z represent the number of the substituents. In
addition, p is an integer of 0 to 3, q is an integer of 1 to 3, and r is
an integer of 0 to 3.

[0103]The foregoing A is selected from the group consisting of, for
example, hydrogen, halogen, a C1 to C3 alkyl group, a C1
to C3 halogenated alkyl group, an alkoxy group denoted by OR (here,
R is at least one species of a C1 to C3 alkyl group and a
C1 to C3 halogenated alkyl group and is positioned at a meta
position or a para position with respect to a carbonyl functional group
or a group Y), an aryl group, a substituted aryl group by halogenation or
the like, a C1 to C9 alkoxycarbonyl group, a C1 to C9
alkylcarbonyloxy group, a C1 to C12 aryloxycarbonyl group, a
C1 to C12 arylcarbonyloxy group and a substituted derivative
thereof, a C1 to C12 arylcarbamoyl group, a C1 to C12
arylcarbonylamino group and a substituted derivative thereof. When number
of the foregoing As is two or more, these As are the same or different.
The foregoing A: is selected from the group consisting of, for example,
halogen, a C1 to C3 alkyl group, a C1 to C3
halogenated alkyl group, a phenyl group and a substituted phenyl group,
and when number of the foregoing A's is two or more, these A's are the
same or different. Examples of a substituent of the foregoing substituted
phenyl group include halogen, a C1 to C3 alkyl group, a C1
to C3 halogenated alkyl group and combinations thereof. The
foregoing subscript t is an integer of 0 to 4 and the foregoing subscript
z is an integer of 0 to 3.

[0104]Among the repeat units of polyamide or polyester, expressed by the
formula (22), a repeat unit expressed by the following general formula
(23) is preferred.

##STR00012##

[0105]In the formula (23), A, A' and Y are identical to those of the
foregoing formula (22), and the subscript v is an integer of 0 to 3,
preferably an integer of 0 to 2. The subscripts x and y are 0 or 1,
respectively (however, x and y are not simultaneously 0).

[0106]The above-mentioned optical compensation plate is generally formed
on an appropriate substrate.

[0107]The substrate is not particularly limited, but substrate films
having excellent transparency which can be used as a protective film of a
polarizer are preferred. Further, as the substrate film, films containing
a thermoplastic resin are preferred since these films are suitable for a
stretching treatment or a shrinkage treatment. Specific examples of the
substrate film include acetate resins such as triacetyl cellulose (TAC),
polyester resins, polyethersulfone resins, polysulfone resins,
polycarbonate resins, polyamide resins, polyimide resins, polyolefin
resins, acrylic resins, polynorbornene resins, cellulose resins,
polyarylate resins, polystyrene resins, polyvinyl alcohol resins,
polyvinyl chloride resins, polyvinylidene chloride resins, polyacrylic
resins, mixtures thereof and the like. Also, liquid crystal polymers can
be used. Further, as described in, for example, Japanese Unexamined
Patent Publication No. 2001-343529, a mixture of a thermoplastic resin
having a substituted imide group or a non-substituted imide group on the
side chain and a thermoplastic resin having a substituted phenyl group or
a non-substituted phenyl group and a nitrile group on the side chain can
also be used. Specific examples of this mixture include a resin
composition having an alternating copolymer consisting of isobutene and
N-methylenemaleimide, and an acrylonitrile-styrene copolymer. Among
these, a material, which can set the birefringence obtained, for example,
in forming a transparent film, at a relatively lower level, is preferred,
and specifically, the above-mentioned mixture of a thermoplastic resin
having a substituted imide group or a non-substituted imide group on the
side chain and a thermoplastic resin having a substituted phenyl group or
a non-substituted phenyl group and a nitrile group on the side chain is
preferred. A thickness of the substrate film can be appropriately
determined, but it is preferably about 5 to 300 μm, and more
preferably in the range of 5 to 150 μm.

[0108]In addition, preferably, the foregoing substrate film would not be,
for example, colored. Specifically, the retardation Rth in a thickness
direction of the film expressed by the following equation:
Rth=[(nx+ny)/2-nz]d, is preferably in a range of -90 nm to +75 nm, more
preferably in a range of -80 nm to +60 nm, and particularly preferably in
a range of -70 nm to +45 nm. When the retardation in a thickness
direction is in a range of -90 nm to +75 nm, coloring (optical coloring)
resulting from a film can be resolved. However, nx and ny represent the
refractive indexes in the directions orthogonal to each other in a plane
of the substrate film, and nz represents the refractive index in a
thickness direction, and d represents a thickness (nm).

[0109]Since the substrate film can be used as a protective film of a
polarizer, it is also preferred to use acetate resins such as triacetyl
cellulose (TAC) or norbornene resins. The optical film obtained by
forming the optical compensation plate directly on this substrate film
can constitute a polarizing plate when a polarizer is laminated on the
optical film.

[0110]Next, a production method of the optical compensation plate, a
thickness of which does not have a uniform distribution, of the present
invention will be described.

[0111]The optical compensation plate of the present invention is not
particularly limited in the production method thereof as long as it can
be formed in such a way that a layer thickness becomes thin toward a
central portion, and for example, the optical compensation plate can be
prepared by applying a material for forming an optical compensation plate
onto an appropriate substrate while controlling an applied thickness. The
material for forming an optical compensation plate is not particularly
limited as long as it is a birefringent material exhibiting a
birefringent property after forming the optical compensation plate, and
non-liquid crystal polymers such as polyimide, described above in detail,
can be employed, but in addition a liquid crystal polymer can also be
employed.

[0112]Incidentally, specific control techniques of the applied thickness
will be described later.

[0113]As the substrate, the above-mentioned substrate film is preferably
used. By applying the birefringent material directly onto such substrate
film, an optical film in which the optical compensation plate is directly
laminated on the substrate film to become the protective film of the
polarizer can be obtained.

[0114]A method of applying the birefringent material for forming the
optical compensation plate onto the substrate film is not particularly
limited. Examples of the method of applying include a method of heating
and melting a birefringent material (for example, non-liquid crystal
polymer such as polyimide) to apply this material, and a method of
preparing a birefringent material in solution form for application. Among
others, a method of applying a polymer solution formed by dissolving the
above-mentioned non-liquid crystal polymer as a birefringent material in
a solvent is preferred because of excellent workability.

[0115]A polymer concentration in the above-mentioned polymer solution is
not particularly limited, but the concentration of the non-liquid crystal
polymer is preferably 5 to 50 parts by weight, and more preferably 10 to
40 parts by weight with respect to 100 parts by weight of the solvent
since the polymer solution of this concentration has a viscosity which is
superior in an applying property. In addition, when applying the polymer
solution with a die coater described later, as the polymer concentration
in the polymer solution, the concentration of the non-liquid crystal
polymer is preferably 10 to 35 parts by weight, and more preferably 10 to
25 parts by weight with respect to 100 parts by weight of the solvent.

[0116]The viscosity of the polymer solution is preferably 100 to 2000
mPasec, more preferably 200 to 1800 mPasec, and particularly preferably
500 to 1500 mPasec. When the polymer solution, in which the viscosity is
adjusted to a range of 100 to 2000 mPasec, is used, a defect of
appearance due to the fluidization of the solution during the time
between the completion of applying and the drying step can be further
inhibited and it is possible to prevent air bubbles from penetrating into
the optical compensation plate to be obtained.

[0117]The solvent of the polymer solution is not particularly limited as
long as it can dissolve a birefringent material such as a non-liquid
crystal polymer, and it can be appropriately determined in accordance
with the species of the birefringent material. Specific examples of the
solvent include halogenated hydrocarbons such as chloroform,
dichloromethane, carbon tetrachloride, dichloroethane, tetrachloroethane,
trichloroethylene, tetrachloroethylene, chlorobenzene and
o-dichlorobenzene; phenols such as phenol and p-chlorophenol; aromatic
hydrocarbons such as benzene, toluene, xylene, methoxybenzene and
1,2-dimethoxybenzene; ketone solvents such as acetone, methyl ethyl
ketone, methyl isobutyl ketone, cyclohexanone, cyclopentanone,
2-pyrrolidone and N-methyl-2-pyrrolidone; ester solvents such as ethyl
acetate and butyl acetate; alcohol solvents such as t-butyl alcohol,
glycerin, ethylene glycol, triethylene glycol, ethylene glycol monomethyl
ether, diethylene glycol dimethyl ether, propylene glycol, dipropylene
glycol and 2-methyl-2,4-pentanediol; amide solvents such as
dimethylformamide and dimethylacetamide; nitrile solvents such as
acetonitrile and butyronitrile; ether solvents such as diethyl ether,
dibutyl ether and tetrahydrofuran; carbon disulfide; ethyl cellosolve,
butyl cellosolve; and the like. These solvents may be used singly or in
combination of two or more species. In addition, in the present
invention, methyl isobutyl ketone is particularly preferred since it has
a high dissolving property for the non-liquid crystal polymer and does
not corrode the substrate film.

[0118]The polymer solution may be further mixed with various additives
such as a stabilizer, a plasticizer and metals as required.

[0119]In addition, the polymer solution may contain, for example,
different another resin within the bounds of not significantly
deteriorating an aligning property of a birefringent material. Examples
of the another resin include various general purpose resins, engineering
plastics, thermoplastic resins, and thermosetting resins.

[0121]When the another resin is thus mixed in the polymer solution, an
amount of the another resin to be mixed is, for example, 0 to 50% by
weight with respect to the foregoing polymer material, and preferably 0
to 30% by weight.

[0122]A method of applying the above-mentioned polymer solution is not
particularly limited as long as it is a method by which a thickness of an
applied film can be controlled. Examples of the method of applying
include a die coating method, and a gravure printing method, but it is
preferred to coat by the die coating method since a thickness can be
easily controlled. A thickness of an applied film can be easily adjusted
by changing a pitch of a discharge port in accordance with the die
coating method.

[0123]An example of a die coater apparatus 10 used for producing the
optical compensation plate of the present invention, which can adjust a
thickness of an applied film, is shown in FIG. 4.

[0124]This die coater apparatus 10 includes a slot die 11 to discharge a
material, and a rotating roller 12 to feed a long substrate film 20
(original film). The slot die 11 has a discharge port 18 in parallel with
a rotation axis of the rotating roller 12, and is located at a position
opposed to the rotating roller 12. The rotating roller 12 comprises a
rotatable cylindrical body with a wider width than that of the long
substrate film 20, and the long substrate film 20 is wound around the
roller. The width of the substrate film 20 is not particularly limited,
but a width matching the width of the liquid crystal cell to which the
optical compensation plate of the present invention is attached is
preferred. The width of the substrate film 20, for example, can be set
about 600 mm to 1500 mm can be used.

[0125]As shown in FIGS. 4 to 6, the slot die 11 includes a pair of upper
and lower die bodies 13, 14 combined into one through a tightening tool
(not shown) such as a bolt, and a shim 15 shaped like a letter U in a top
view, interposed between the pair of upper and lower die bodies 13, 14.

[0126]A top face of the upper die body 13 is provided with a groove shaped
like a letter U in a width direction. In the groove portion 13a, a
plurality of actuators 16 are installed at prescribed pitches in the
width direction. This actuator 16 can stretch in a direction orthogonal
to the width direction of the die body 13, and it can be stretched and
retracted using, for example, a cylinder driven hydraulically or by air
pressure.

[0127]A feed opening 14a to feed the above-mentioned birefringent material
(for example, the above-mentioned polymer solution formed by dissolving
the non-liquid crystal polymer in a solvent) is formed at the backside of
the lower die body 14. In addition, a manifold 14b in the form of a slit
is opened in the inner face of the lower die body 14. This manifold 14b
is communicated with the foregoing feed opening 14a, and opened in the
form of a slit extending in the width direction.

[0128]Within the upper and lower die bodies 13, 14 combined into one with
the shim 15 therebetween, a cavity 17 communicated with the manifold 14b
is formed. The discharge port 18 corresponding a thickness of the shim
15, extending in the width direction, is formed in the front face of the
pair of die bodies 13, 14.

[0129]In the above-mentioned slot die 11, a front portion of the upper die
body 13 can be bent down around a corner 13b of the groove portion 13a as
a fulcrum by stretching of the actuator 16. As a result of this, an
opening distance (vertical clearance) of the discharge port 18 becomes
small in response to the stretched actuator 16.

[0130]Therefore, as shown in FIG. 7B, by stretching the actuator 16'
positioned at a central portion at the maximum stroke, and stretching the
actuators 16'' positioned at outer sides of the actuator 16' less than
the actuator 16', a front end of the upper die body 13 can be deformed to
a mild curve which is convex downward. Therefore, it is possible to
adjust the opening distance of the discharge port 18 so as to become
small gradually toward the central portion from both end portions in a
lateral direction (in FIGS. 7A and 7B, the discharge port 18 is filled
with tint black for convenience).

[0131]The above-mentioned die coater apparatus 10 pushes a birefringent
material 21 out from the discharge port 18 as shown in FIG. 8. The
birefringent material 21 pushed out can be applied continuously to the
long substrate film 20 fed by the roller 12 longitudinally to form an
applied film on the substrate film 20. In forming the applied film, as
described above, by appropriately extending each actuator 16 to adjust
the opening distance of the discharge port 18 so as to become small
toward the center, an applied film, which becomes thin gradually toward a
central portion from both end portions in a lateral direction of the
substrate film 20, can be produced.

[0132]If the above-mentioned die coater apparatus 10 is used, by
appropriately adjusting the degree of extension of the actuator 16, it
becomes possible to control the distribution of a thickness of the
applied film easily and as desired.

[0133]Further, by placing more actuators 16, it becomes possible to adjust
the opening distance of the discharge port 18 more finely.

[0134]Further, a running velocity (feeding velocity) of the long substrate
film 20 and a pressure to discharge the birefringent material 21 are not
particularly limited. Generally, when the substrate film 20 is fed fast,
the birefringent material 21 can be applied thin as a whole.

[0135]As the specific running velocity (feeding velocity) of the substrate
film 20, 10 to 300 m/min can be exemplified, further 10 to 100 m/min is
preferred, and particularly 10 to 50 m/min is more preferred. The reason
for this is that when the running velocity of the substrate film 20 is in
a range of 10 to 300 m/min, the discharge of a solution from the
discharge port 18 of the die is stable and an applied film (namely an
optical compensation plate) excellent in thickness precision can be
formed. However, even when the running velocity is changed, the applied
film can be still formed in such a way that a thickness in the central
portion in the width direction of the substrate film 20 is thinner than
those in both ends portion.

[0136]A coefficient of variation of the running velocity of the substrate
film 20 is preferably controlled so as to be 3.0% or less. By limiting
the coefficient of variation of the running velocity to 3.0% or less,
applying of the birefringent material to the substrate film 20 is
stabilized, and an applied film without unevenness (projections or
depressions in the form of a streak in a width direction are not
produced) can be formed. Preferably, the lower limit of the
above-mentioned coefficient of variation is theoretically 0%, but
practically 0.5%, and more preferably 0.9%.

[0137]The coefficient of variation of the running velocity can be
determined by running the substrate film continuously for 60 seconds
using, for example, "Laser Speed System Model LS200" (manufactured by
KANOMAX JAPAN, INC.), measuring a running velocity every 8 second,
plotting each velocity in a table, determining the maximum value X1, the
minimum value X2, an average AV of the running velocity from this table,
and calculating the coefficient of variation from the following equation.

Coefficient of variation={[(X1-X2)/AV]/2}×100

[0138]Next, FIGS. 9A and 9B show a variation example of the die coater
apparatus.

[0139]In the slot die 11 of this variation example, the opening distance
of the discharge port 18 is formed in advance so as to become small
toward the central portion by grinding a bottom surface of a front
portion of the upper die body 13 (and/or the lower die body 14) in the
form of a side of a cylinder.

[0140]Also when the birefringent material is applied using a die coater
apparatus provided with the slot die 11 of this variation example, it is
possible to apply the birefringent material so as to become thin toward a
central portion from both end portions in a lateral direction of the
substrate film as with the above case.

[0141]In addition, although not shown, a die coater apparatus using a shim
formed so as to become thin toward a central portion in a lateral
direction, or a die coater apparatus in which the opening distance of the
discharge port is controlled by adjusting a tightening force of the upper
and the lower die bodies may be used. Also when such a die coater
apparatus is used, it is possible to apply the birefringent material so
as to become thin toward a central portion from both end portions in a
lateral direction of the substrate film as with the above case.

[0142]An applied film, in which a thickness distribution is adjusted, is
formed by following the above method, and then this applied film is
dried. After drying, an optical film formed by laminating the optical
compensation plate 7 of the present invention directly on the long
substrate film 20 can be obtained. In addition, as shown in FIG. 10, by
cutting this optical film in a width direction of the substrate film 20,
a rectangular optical film can be obtained. In this rectangular optical
film, the optical compensation plate 7 becomes thin toward a central
portion from both end portions in a lateral direction (a width direction
of the substrate film 20). The optical compensation plate 7 is bonded to
a liquid crystal cell with the vertical and horizontal sides of the
optical compensation plate aligned with those of the liquid crystal cell
and used.

[0143]In addition, in the above-mentioned substrate film, transparent
films such as a TAC film exemplified in the above description can be
employed. As a film of this kind, a film having a shrinking property in
one direction in a plane of a film as thermal properties is preferred.
The reason for this is that by using such the substrate film, the optical
compensation plate exhibiting the optically biaxial property can be
readily produced.

[0144]Specifically, the above-mentioned non-liquid crystal polymer like
polyimide exhibits an optical property of nx≈ny>nz by its
nature regardless of the presence or absence of alignment of the
substrate film. Therefore, an applied film containing the non-liquid
crystal polymer exhibits an optically uniaxial property. That is, the
applied film exhibits retardation only in a thickness direction. Herein,
by using a film to shrink in one direction in a plane of a film as a
substrate film, the applied film on the substrate film shrinks in the
plane as the substrate film shrinks. Accordingly, difference of
refraction in the plane is produced in the applied film, and the optical
compensation plate exhibiting the optically biaxial property
(nx>ny>nz) can be obtained.

[0145]The above-mentioned substrate film is preferably stretched in
advance, for example, in any one direction in a plane of a film in order
to have a shrinking property in one direction in the plane. By stretching
the film in advance like this, a shrinking force is generated in a
direction opposite to the foregoing direction of stretching. The
difference between shrinkages in the plane of this substrate film is used
to impart the difference between refractive indexes in the plane to the
non-liquid crystal material of the applied film.

[0146]A thickness of a not-yet-stretched substrate film is not
particularly limited, but the thickness is, for example, in a range of 10
to 200 μm, preferably in a range of 20 to 150 μm, and particularly
preferably in a range of 30 to 100 μm. In addition, a stretch ratio is
not particularly limited as long as the optical compensation plate formed
on the shrunken substrate film falls within a range of exhibiting the
optically biaxial property (nx>ny>nz).

[0147]The substrate film subjected to a stretching treatment is generally
shrinks by heating. Accordingly, by applying a heating treatment to the
applied film on the above-mentioned substrate film, the substrate film is
shrunk. The applied film shrinks in association with this shrinkage of
the substrate film, and thereby the optical compensation plate having the
optically biaxial property can be formed. The conditions of the heating
treatment are not particularly limited, and they can be appropriately
determined according to the species of a material of the substrate film.
Generally, a heating temperature is, for example, in a range of 25 to
300° C., preferably in a range of 50 to 200° C., and
particularly preferably in a range of 60 to 180° C.

[0148]Optical properties of the optical compensation plate may varies with
time in proportion to an amount of a solvent remaining in the optical
compensation plate. Therefore, the amount of a solvent remaining in the
optical compensation plate to be obtained is, for example, preferably 5%
by weight or less, more preferably 2% by weight or less, and furthermore
preferably 0.2% by weight or less.

[0149]As a method of forming the optical compensation plate exhibiting the
optically biaxial property (nx>ny>nz) on the substrate film, the
following method is also effective. That is, the above-mentioned
birefringent material is applied directly onto the substrate film to form
an applied film, and then the substrate film and the applied film are
stretched together. This method does not use a shrinking force of the
substrate film, but the optical compensation plate exhibiting the
optically biaxial property (nx>ny>nz) can be formed directly on the
substrate film on the same principle as in the above description even by
this method.

[0150]The above-mentioned method of stretching the laminate of the
substrate film and the applied film is not particularly limited. Examples
of the stretching method include a method of stretching in a width
direction with a tenter, a free-end longitudinal stretching method of
uniaxially stretching in a longitudinal direction of the substrate film,
a fixed-end transverse stretching method of uniaxially stretching in a
width direction with the substrate film fixed in a longitudinal
direction, and a biaxial stretching method of sequential or simultaneous
stretching in both a longitudinal direction and a width direction.
Preferably, by stretching the laminate in a width direction with a tenter
method, and then shrinking it at a stretch ratio of 0.9 or more and less
than 1 in a width direction, variations in an alignment axis (slow axis)
can be made extremely small.

[0151]In addition, stretching of the laminate of the substrate film and
the applied film may be performed, for example, by stretching both of the
substrate film and the applied film, but it is preferred to stretch only
the substrate film from the following reason. When stretching only the
substrate film, the applied film is indirectly stretched due to tension
produced in the substrate film by this stretching. In addition,
generally, stretching of a single layer is more uniform than stretching
of a laminate, and therefore by stretching uniformly only the substrate
film, the applied film can also be uniformly stretched.

[0152]The conditions of stretching the laminate is not particularly
limited, and they can be appropriately determined in accordance with, for
example, species of the substrate film or the materials for forming the
optical compensation plate. As a specific example, a stretch ratio is
preferably more than 1 and 5 or less, more preferably more than 1 and 4
or less, and particularly preferably more than 1 and 3 or less.

[0153]The optical film (laminated body of the substrate film and the
optical compensation plate) obtained by the above method satisfies the
conditions of the following equations (I) to (III). Particularly, by
satisfying the equation (I), it is possible to prevent rainbow
irregularity (a phenomenon in which a screen is colored in multiple
colors) posed when the optical film is located in a liquid crystal
display device.

Δn(a)>Δn(b)×10 Equation (I)

1<(nx-nz)/(nx-ny) Equation (II)

0.0005<Δn(a)≦0.5 Equation (III)

[0154]In the equations (I) and (III), Δn(a) is the birefringence of
the optical compensation plate, and Δn(b) is the birefringence of
the substrate film, and these are expressed by the following equations,
respectively. In the equation (II) and the following equation, nx, ny,
and nz represent the refractive indexes in the directions of an X-axis, a
Y-axis and a Z-axis, respectively, in the optical compensation plate and
nx', ny', and nz' represent the refractive indexes in the directions of
an X-axis, a Y-axis and a Z-axis, respectively, in the substrate film,
and the X-axis is an axial direction in which the maximum refractive
index is shown in planes of the compensation plate and the substrate
film, the Y-axis is an axial direction perpendicular to the X-axis in the
foregoing planes, and the Z-axis represents a thickness direction
perpendicular to the X-axis and the Y-axis.

Δn(a)=[(nx+ny)/2]-nz

Δn(b)=[(nx'+ny')/2]-nz'

[0155]Further, the optical film prepared by laminating the optical
compensation plate on the substrate film preferably has at least one of
an adhesive layer and a pressure sensitive adhesive layer. The reason for
this is that by providing the adhesive layer or the like, bonding of the
optical film and other optical members such as a polarizer or other
members such as a liquid crystal cell becomes easy. Therefore, the
adhesive layer or the pressure sensitive adhesive layer is preferably
provided on the outermost face of the optical film. Further, the adhesive
layer or the pressure sensitive adhesive layer may be provided on the
outermost one side or on the outermost both sides of the optical film.

[0156]A material of the pressure sensitive adhesive layer (or the adhesive
layer) is not particularly limited, and for example, polymer based
pressure sensitive adhesives such as acrylic, vinyl alcohol, silicone,
polyester, polyurethane, and polyether pressure sensitive adhesives,
rubber pressure sensitive adhesives, other pressure sensitive adhesives,
and adhesives can be used. In addition, by including fine particles in
these materials, a layer exhibiting a light diffusing property may be
formed. As the pressure sensitive adhesive or the adhesive, materials
having, for example, excellent hygroscopicity or excellent heat
resistance are preferred. When such materials are used for, for example,
a liquid crystal display device, it is possible to prevent foaming or
peeling due to absorption of moisture, deterioration of optical
properties due to the difference in thermal expansions, and warp of the
liquid crystal cell. Accordingly, a liquid crystal display device of high
quality, having excellent durability, can be provided.

[0157]The optical compensation plate or the optical film of the present
invention may be used alone. In addition, as required, the optical
compensation plate or the optical film can be combined with other optical
members such as a polarizer to be formed into a laminate and used for
various optical applications.

[0158]For example, since the above-mentioned optical film has a substrate
film and an optical compensation plate, by laminating a polarizer on this
substrate film or optical compensation plate, it is possible to configure
an elliptical polarizing plate. However, since the substrate film can
also be used as a protective film of a polarizer, by laminating the
polarizer on the surface of the substrate film, a low-profile polarizing
plate can be favorably formed.

[0159]A material of the polarizer is not particularly limited, and
conventionally known materials can be used. The polarizer prepared, for
example, by allowing various films to adsorb iodine or a dichroic
material such as a dichroic dye to dye the films and
crosslinking/stretching/drying the dyed films can be used. Among these, a
polarizer having a film, which transmits linearly polarized light when
natural light enters, is preferred, and a polarizer which is superior in
light transmittance and a degree of polarization is particularly
preferred. Examples of a film for adsorbing the foregoing dichroic
material include hydrophilic polymer films such as polyvinyl alcohol
(PVA) films, partially formalized PVA films, ethylene-vinyl acetate
copolymer based partially saponified films and cellulose films. In
addition to these, as the film, for example, aligned polyene films such
as a dehydration product of PVA and a dehydrochlorination product of
polyvinyl chloride can also be used. Among these, PVA films are
preferred. Further, a thickness of the foregoing polarizer is generally 1
to 80 μm, but the thickness is not limited to this.

[0160]The optical compensation plate and the optical film of the present
invention can be used in combination with conventionally known optical
members such as various retardation plates, a diffusion control film, and
a brightness enhancing film in addition to the above-mentioned
polarizers. Examples of the retardation plates include films formed by
uniaxially stretching or biaxially stretching a polymer film, by aligning
a polymer film in a Z-axis direction, and an applied film of a liquid
crystal polymer. Examples of the diffusion control film include films
using diffusing, scattering, and refraction. The diffusion control film
can be used for controlling a viewing angle, glare concerning resolution,
and scattered light. As the brightness enhancing film, a brightness
enhancing film using selective reflection of cholesteric liquid crystal
and a quarter-wave plate (λ/4 plate) or a scattering film using
anisotropic scattering by polarization direction can be used.

[0161]A method of laminating other optical members on the optical
compensation plate and the optical film of the present invention is not
particularly limited, and lamination can be performed by conventionally
known methods. Generally, the same pressure sensitive adhesives and
adhesives as those described above can be used, and their species can be
appropriately determined based on each material. Examples of the
adhesives include polymer based adhesives such as acrylic, vinyl alcohol,
silicone, polyester, polyurethane, and polyether adhesives, and rubber
adhesives. In addition, adhesives comprising water-soluble crosslinking
agents for vinyl alcohol polymers such as glutaraldehyde, melamine and
oxalic acid can also be used. The above-mentioned pressure sensitive
adhesive and adhesive are hard-to-peel, for example, even by effects of
humidity or heat, and are superior in light transmittance and a degree of
polarization. Specifically, when the polarizer is a PVA film, it is
preferred to use a PVA adhesive from the viewpoint of stability of a
bonding treatment. These pressure sensitive adhesives and adhesives may
be applied, for example, directly to the surface of the polarizer or the
substrate film, or a layer such as a tape or a sheet composed of the
foregoing adhesives or pressure sensitive adhesives may be located on the
foregoing surface. A thickness of such adhesive layer is not particularly
limited, but the thickness is, for example, 1 nm to 500 nm, preferably 10
nm to 300 nm, more preferably 20 nm to 100 nm.

[0162]It is also possible to impart ultraviolet absorbing power to the
optical compensation plate and the optical film of the present invention
described above and other optical members laminated thereon. As means for
imparting ultraviolet absorbing power, it can be exemplified that
ultraviolet absorbers such as salicylic acid ester compounds,
benzophenone compounds, benzotriazole compounds, cyanoacrylate compounds,
and nickel complex salt compounds is appropriately treated.

[0163]As described above, the optical compensation plate and the optical
film of the present invention can be located on one side or both sides of
the liquid crystal cell to be used for forming the liquid crystal display
device to be used as a form of a liquid crystal panel. The liquid crystal
panel can be used for reflective, semi-transmissive, or
transmissive-reflective liquid crystal display devices.

[0164]A type of a liquid crystal cell forming the liquid crystal display
device can be arbitrarily selected. Liquid crystal cells of various types
such as an active matrix drive type typified by a thin-film transistor
type and a simple matrix drive type typified by a twisted nematic type
and a super twisted nematic type can be used. Among these, since the
optical compensation plate of the present invention is particularly
superior in optical compensation of a VA (vertical alignment) cell, it is
very useful as a viewing angle compensating film for a VA mode liquid
crystal display device.

[0165]In addition, when the above-mentioned optical compensation plate,
optical film, and polarizer are provided on both sides of the liquid
crystal cell, these may be the same or may be different. Furthermore, in
forming the liquid crystal display device, adequate parts such as a prism
array sheet, a lens array sheet, a light diffuser and a backlight can be
located in one layer or two or more layers at adequate positions.

[0166]Furthermore, when the liquid crystal display device of the present
invention includes a light source such as a backlight, the light source
is preferably a plane light source emitting, for example, polarized light
because optical energy can be effectively used.